Watertight doors are an integral part of all ocean-going ships and this includes gravity type self-unloading ships. What makes these particular watertight doors different from most is that they must close the penetration through which the conveyor must pass. The complexity and size of the door can be rather considerable given: (1) the need for the doors to seal around both the carrying and return runs of the conveyor, and; (2) small leakage rates permitted by IACS, Solas, the regulatory bodies and as standardized in ASTM F1196. Several designs have been introduced by different companies over the years and, whilst functional, some designs tend to be rather complex in terms of ease of operation or mechanical content. Such complexity can require increased maintenance and also lead to a more rapid deterioration of components in one form or another.
In all cases, the conveyor is supported by idler rolls and these idler rolls are located adjacent to, and on both sides of, the watertight door. The conveyor idlers are typically supported on rigid structures called ‘stringers’ that run the length of the conveyor. The watertight door is opened prior to conveyor system start-up and prior to material being placed on the conveyor belt. The watertight door must be closed prior to the vessel leaving port to ensure adequate stability for safety at sea in the event that one of the cargo holds is breached and flooded. Depending upon the design of the watertight door, the conveyor belt can impose a significant force against the watertight door during closing operations and in a closed static case due to residual belt tensions. In the case of at least one watertight door design, a multiple of such conveyor idlers are required to be removed before the watertight door can be closed due to the external force imposed on the door from the belt. In some cases, a ship's crew is required to remove a number of conveyor idlers (typically three) on either side of the door (for a total of six), by hand, before the watertight door can be closed. This is obviously a time consuming and laborious chore.
It would therefore be advantageous to have an improved watertight door system wherein the conveyor belt tensions could be relieved automatically, by attaching a section of the adjoining conveyor support stringers on either side of the door, with those sections hinged to the watertight door, whereby actuation of the door causes the adjoining stringers to move with the door, and the associated conveyor idlers to be lowered out of the way without the removal thereof.
It would be further advantageous to have a watertight door system which can be opened and closed in an efficient, timely manner, and which is of a non-complex design that does not require a multitude of moving components or excessive preventative maintenance. To this end, the present invention effectively addresses this need.